Retractable landing gear



March 10, 1953 A. E. KANODE ETAL 2,630,990

RETRACTABLE LANDING GEAR Filed March l, 1951 4 Sheets-Sheet l March 10, 1953 A. E. KANODE E'rAx.

RETRACTABLE LANDING GEAR 4 Sheets-sheet 2 Filed March l, 1951 ATTORNE March l0, 1953 A. E.=KANDE 'E1-An. 2,630,990

RETRACTABLE LANDING GEAR Filed MaIOh l, 1951 4 Sheets-Sheet 5 A. E. KANODE ET AL 4 Sheets-Sheet 4 Filed March l 1951 Patented Mar. 1Q, 1953 UNITED STATES PATENT OFFICE l2,630,990 RETRACTABLE'LANDING GEAR "of Maryland ApplicarionMarch 1, 1951, seria1No..z13,35s 9 claims. (o1. 2214-102) This invention relates -to aircraft landing gear of the retractable type employing a shock absorbing drag strut.

Many present day aircraft provide shock absorption devices for damping dynamic loads in only the vertical direction, even though it is well recognized that .drag loads due to wheel spin-up when contacting the ground, Vproduce stresses Whichare in many cases even greater in magnitude than are the stresses produced by the vertical loads.

vIn the slower type aircraft where vibration eifects were not critical, or. at least not thought to be. the 'gear and gearfgljsupporting structure could be made suincientlyheavy and rugged to satisfactorily take the .dynamic loads and still be lighter than would result by attempting to dampen the shock loads ithe drag strut by use of conventional shock l,absorbing devices. Higher landing speeds, however, have increased the severity of the shock loads to such anextent that even if thestructure is designed to withstand the magnitude of the applied dynamic loads, the resulting uncontrolled vibrations from Wheel spin-up at ground Contact c ause the metal to work harden Vand becme quite brittle and weak after a short period of use. This eifect is almost impossible'to detect before actual failure has occurred. The great majority of landing gear failures has beenattributed to this very phenomena commonly called fatigue It is among the objects of this invention to provide a retractable :landing gear with a completely self-contained shock-absorbing drag strut which eiectively eliminates structural failures due to uncontrolled `vibrations; and which weightwise favorably compares with the conventional xed strut installations. The light-weight airoil shock absorber of this inventioncooperates with the main oleo to `damp out all vibrator-y oscillations in thegear, permitting substantial weight savings to be realized in the gear reaction structure as wellas in the gear itself.

Another object of this invention `is to provide a retractable landing gear having ashock absorbing drag strut withan automatic up and down lock and compensating mechanism to prevent the gear from collapsing while allowing the shock loads to be properly damped,

Still another object of this invention is to provide a retractableV landing gear having` a shock absorbing drag strut with door opening and closing means operable by movement of the gear adapted to open landing gear doors only While raising andflowe'ring thezgear, and wherein the-shock loads may be properly damped without affecting its operation.

Further and other objects will become vapparent from thefaccompanying description and drawings which form a part of this disclosure and in which like numerals refer to parts. In the drawing: Figure l is a Vperspective viewsof the complete landing vgear of this irventio carried by wing structure of an aircraft. Figure 2 is a-seotinnal sorbing drag strut,

Figure 3v is aside. View of the upand down lock mechanism.

Figure 4 is a .fragmentary side view of the compensating vrnechar i e Figure 5 is aside viewoff the-door opening and closing mechanism -inbo positions ofthe gear.

Figure 6 is a sectional view taken on the line 6-'6 of Figure 5. l

th that ab- In Figure vl, fdrpurposs ofdescription, landing gear l is shown carried by the wing of an' aircraftoutboard of the fuselage as noted by the wing frontspar .and reinforcing structure 2. Main oleo 4 is pivotally carried in a conventional manner as at 'by a p ai r of V- shaped brackets 6, rigidly yconnecting with the structure 2. 'Iheglowerendof adapted to rotatably supportati) with respect to the supporting structure f or cushioningvertical loads ofthe aircraft. 1 o prevent main oleo I from swinging freely about its pivot, a `drag strut 8 ispinned at Q to a bracket I carried rby main oleo Il and is swingably carried atits'opposte end by pin Il rigidly carried by the front spar structure 2. Drag strut 8, being `of the shock absorbing typegis specially adapted to control the vibrations set Vup in the gear due mainly to wheel `spin-up at ground contact. As generally show n in Figure l, drag strut 8 is 1a toggle .linkagev formed of two members,` one being the shockxabsorbing unit l2, and the other being a swingable extension I3 ofthe shock absorbing whereinl the swingable memberand shockabsorber are joined by means Ofpinll. Shook absorber I2 employs air and o il to absorb vthe shock loads -in a self-contained two chamber system which results in a light-weight construction permitting--anreiiicient landing gear design. As shownI in Figure 2; tubular housing I5: ofshock absorber '|2is'1provided`with a gerrerally cylindricalv bore lis adapted to' receive a tubular partition member t6, which extends part-way through the length of the bore and is ixedly carried therein by an abutment l5 and nut I6'. A bulkhead il', forming an integral part of partition member IS engages the inner wall of bore I8 of housing I5 toiform a piston chamber -lfand an annular reservoir chamber 20. Partition member i6 is provided with an axial bore 2l extending therethrough adapted to slidably receive a piston rod 22 which extends from a pivot connection with pin li at end @t into piston chamber i9. Member 22 is provided with a reduced diametral portion 22 to reduce the frictionai resistance to axial movement through bore 2|. A stepped piston 23 is rigidly carried by piston rod 22 within chamber i9. Stepped piston 23, is provided with a hollow extension 2B forming the step wherein its diameter is larger than the diameter of rod 22 on the opposite side of piston 23, but is of a lesser diameter than the diameter of the piston. Extension 2d is adapted to be slidably received in a bore 2?: in housing l5 to help guide the axial movement of piston rod 22 in absorbing shock loads and also toproduce a change in the volume of piston chamber i5 as rod 22 is moved through its limited axial distance. Piston rod 22 being supported by several bearing surfaces throughout its length greatly increases the ability of the shock absorber to withstand high bending loads. Suitable sealing means are provided as at 2t to insure fluid tight piston and reservoir chambers. An oriiice 2; is formed in bulkhead Il so as to allow fluid cornmunication between the two chambers. A large orice 28 and a small oriice 28 are formed in piston 23 to allow fluid to pass through to either side of the piston. Orice 2S is of the one-way type adapted to permit the flow of fluid therethrough from the reservoir side of the piston chamber to the opposite side of the piston, but will not permit flow therethrough in the other direction. Orifice 28 allows the ow of iiuid in either direction. A valve 29 communicating,r with reservoir chamber through housing i5 provides a means for filling both chambers with fluid and also for forcing air under pressure into the reservoir chamber. The air is under sufficient pressure to resist the static forces while the oil is employed to cushion the dynamic loads. rEhe area on one side of the piston being larger than on the other side, it is obvious that the normal no load position of the piston is as shown in Figure 2, resting against the bottom or" the bore in housing l5. Thus it is obvious that the shock absorber specifically described is adapted to function where the initial shock load produces tension in the drag strut.

For the shock absorber to function properly, the piston chamber must always be full of oil. Because the uid volume of the piston chamber varies with the axial movement of piston member 22, the size of the orifices relative to one another is important if this condition is to be maintained. Thus the flow of uid through oriiice 2l must have a ratio with the ilow of fluid through -orices 28 and 28' equal to or less than the ratio of the smallest piston chamber volume to the difference between the smallest piston chamber Volume and the largest piston chamber volume. Also, the flow of fluid through orice 28' must be less than the flow of uid through orifice 21. By varying the size of these orifices, keeping of course, within the required relationship, a considerable variation 4 in the amount of damping action can be attained. Damping effect in one direction can be made greater or less than the damping effect in the opposite direction. Though the use of two orifices in the piston is the simplest Way of obtaining the proper shock absorption, it is believed obvious that one orice would sufice So long as the proper ratio of that oriiice to the oriice in bulkhead l1 was maintained so as to keep the reservoir chamber lilled with fluid under all operating conditions.

To positively control the raising and lowering of landing gear l and to hold it in the fully retracted and extended positions, a locking mechanism 3l is provided as best shown in Figure 3. Locking mechanism 3| is pivotally carried at one end by main oleo il through brackets 32 formed integral therewith and extends to pivotally engage pin lll joining the swingable extension member i3 of the drag strut with the shock absorber I2. Locking mechanism 3l includes two members 33 and 3A forming a toggle type linkage, pivotaliy connected to one another at 35. The pivots about which the components of the landing gear are adapted to swing are so arranged that when the gear is locked in the down position, members 33 and 3d of the locking mechanism are in coaxial alignment as are the two members of the drag strut. The gear iS also adapted for movement so that the two members 33 and 3G of'locking mechanism 3l are again in coaxial relationship when the gear is fully retracted, thus also locking it in that position. Member 33 of locking mechanism 3l is pivotally carried by brackets 32 on main oleo t through a crank shaft 36 which is suitably rotatably supported in brackets 32. An arm 3? is rotationally rigid with crank shaft 35 so that rotation of the crank shaft will cause axial movement of a pin 38 adapted to lock and unlock members S3 and 34 in their co-axial position when the gear is fully up and fully down. Pin 38 is carried within a guide 39 forming an integral part of member 33. Guide 39 is provided with suitable spring mea-ns (not shown) which tends to maintain pin S8 in its fully extended position shown in Figure 3. Link il pivotally connects with pin 38 at lli and with arm 3l through a pin 132 and slot 5.3 arrangement. The use of slot i3 in member 4! is necessary to allow pin 3S to remain retracted during the up and down movement of the gear. Since pin 38 is spring loaded so as to have a tendency to remain in a fully extended position, a cam 44 is provided on member 3a which contacts the end of pin 38 to hold it in its retracted position when the members 33 and 3d are not in their coaxial positions required for the locked condition. A tension bungee spring 45 is pivotally connected at .6 to housing l5 on shock absorber I2 and at 4'! to a protrusion 43 on member 34 rigidly extending beyond pin ifi. Spring d5 tends to maintain members 33 and 3e in their locked co-axial position. A compression bungee spring 59 is pivotally carried at 5i! on, member 33 and also at 5l to a lever 52, rotationally rigid with crank shaft 33. When crank shaft 36 is rotated so as to retract pin 38, lever 52 causes bungee 49 to overpower tension bungee spring e5 and thus cause members 33 and 3ft to swing about pivot 35 from their coaxia1 relationship for unlocking the gear.

The power means to raise and lower the gear is provided by a conventional hydraulically actuated retracting cylinder 53 as shown in Figure 1 wherein 5e and 55: designate fluid lines into the retracting cylinder .necessary to both raise and lower the gear. .The gear .retracting piston rod 56 extends from Within the retracting'cylinder 53 to pivotally engage crank shaft 3S at pin 5i as shown in Figure 3. When piston rod B .is in'its normally extended position, crank shaft 3S is so positioned as to 'allow pin 38 to lock the gear in its down position after `bungee spring 45 vcauses members 33 and 3d to moveinto their co-axial positions. When the'gear retracting piston rod 56 .is in its normally retracted position with the gear up, crankshaft .SS is so positioned as to, again allow pin 38 to lock the two members Stand `Sli in their co-axial positions.

vSince Ashock absorbing drag vstrut 8 ypermits limited swinging movement of main oleo I due to the axial movement between `piston member v25.1 -andhousing i5 in absorbing the shock loads,.ii the upper end of retracting cylinder .lili were yixedly connected to aircraft structuresuch gear Ymovement would obviously cause rotation or" crank shaft .Sii which would in turn unlock the gear. Therefore a compensating Hmechanism as best shown in Figure .e must beemployed toinsure that retracting cylinder 53 moves with the movement of the gear due to shock loads. This is provided for by a link arrangement operated by relative movement between piston member 22 and housing i5 of shock absorber i2 in drag strut 8. A collar 58 is xedly connected to housing i5 of shock absorber l2 and is provided with a stub member 553 adapted to pivotally connect with a link Si? at ti. Link @El extends substantially parallel to piston member 22 to pivotally connect with an arm t2 of a bell crank 63 by means of pin eil. Bell crank G3 is adapted to pivot about pin H which also supports piston member l of shock absorber i5. Thus it is seen that relative movement between piston member 22 and 'nousn ing l5 of shock absorber |42 will cause proportionate movement of bell crank t3. The other arm S5 of bell crank 63 pivotally engages a second link te through pin 67. The opposite end of link de engages a pin E8 on an arm t of a second bell crank l. Bellcrank 'illy is adapted to pivot about pin ll which is held xed with respect to pin il by means of a bracket'l. The other arm l3nt hell crank 'Hl pivotally carries gear retracting cylinder 53 by means of pin i3. With this mechanism, theaxial movement in drag strut 8 is compensated for so as to maintain the distance between pin i3 and pivot E? substantially constant, thereby insuring proper operation of locking mechanism 3l.

Landing gear l, in its retracted position is adapted to be completely confined within the contour of the aircraft. Therefore, it is necessary to employ a system whereby doors'open to permit vraising and lowering of the gear. it is also desirablethat the airplane configuration be as clean aspossible even'withthegear extended. To'obtain this result, it is necessary that the doors open only while thegear is beingmoved nfromthe fully retractedposition to the fully eX- tended position and vice versa. VSuch a system is incorporated in this landing gear as shown in Figure 1 wherein the movement of the gear is caused-to open and close doors '74 and l5 which are hinged to swing about axes located approximately along the upper edge'as at 'lll'o door l.

The doors 'ifi'and-'lli in closedjposition as shown 'in-Figure l mate with one-another at l'-'tov forni a "completely enclosed compartment-*within the connnes'of the aircraft for stowing the gear. A

Asmall 'ap 18, Which'is adapted to movewvithv G2 which is connected -topivot y pin lS l main oleo 4, covers theportionxofthe opening not .coveredby idoors T4.;and"l5. Since iap 'i8 is .not adapted `to -close when the gear `is down, movements `of Vthe :gear due to the `use of the shock absorbing drag vstrut18 donot adversely affect its operation. However, since'doors 'le and limusti remain 'closed while .the gear is down, it is necessary to employ a linkage system which will maintain a uconstant force tending to close -the doorsirrespective ofiaxial movement of drag strut 8. This is accomplished through. aspringyloaded leversystem Vas vbest .shown in Figures 5 and 6.

A ,pairof vbrackets vas '19, .rigidly connecting with main oleo lt, extend forwardlythereof, as shown in Figure `1, .to connect withapair of rod members as Si! which are'adapted tornove axially in one direction Yto open the doors 'Id'and I5 and to'move in the opposte-direction'to lclose the doors whileeither lowering'or raising the gear. Rods `8B pivotally engage va pair of bel1crank-like .members Si as :shown vin Figure 1. The movement of members 8l is such as tofopen Yand close the doors 'le and 75 through :suitable linkages 82. Member'Z of linkage'az .extends forwardly to similarly connectwith thedoor at its forward end. To prevent the" closing `force Aon the doors from becoming excessively-high, when Athe drag strut 8 moves axially to absorb shock loads, the movement of each door is controlled by a rod member 8i) which engages the tip portion le of bracket li) through aslot'fandpin 8:1 arrangement, best shown in .Figure 5. The tipy portion is of bracket 'l-Qis adapted topivotabout pin d to allow the necessary movement inthe mechanism. A bell crank t85 adapted to pivot about pin et on 'armi-87 of bracket `1.9,l also `engages pin Se to control the positionV of -therpin with respect to its slot 83. Anabutment 96 on bracket le limits the movement vof bell crank l85. A link 3B pivotally connects with bell crank 35 through pin 89. The position of the bell crank is controlled by movementr of link-.88 :to insure proper closing of the doors whileA the gearzis extended. A second linked pivotallyconnects Withlink-SS at 9| and is pivoted at its .opposite end to the-'main gear pivot pin 5. The necessary force to keep the door closed is emplied'through link S8 `by spring Tension in spring92 is obtained-'byhooking its vlower V'end et into an eye bolt -94 Von bracket le. Eye Vbolt -Ql is adjustablefso asto increase or decrease the tension-force inspring 92. The force applied to bell crank 85 -by such amechanism will, as seen in Figure 5, tend .to rotate ,the bell'crank about pivot 83 in a counterclockwise ldirection so that it jwill butt against :abutment 95. The. relationship between member- 86, bracket le and bell .crank 35 is most clearly shown inFigure 6 whore- '.tion, the dooris held -in-closedposition byav rigid mechanical linkage. This is necessary to prevent the doors from swingingopen when maneuvering the aircraft duringiiightin such a manner .as to .produce high inertia forces ...tending .to open them.

To lower kthe landing. gear, retracting cylinder .53 is actuate'dso asto axially. move member to an extended position. "The initial movementof member "5t causesrotation'of crankshaft 36l` ina 'direction vto Aretract pin-"StandV loadrcompression 'tbungee spring 119 nso ras v"to -0v1`p0WeT Tension bungee 45 and cause members 33 and 34 to move out of their co-axially aligned locking position, thus starting the gear in its downward motion. As the gear moves down, the first movement of rod a will open the doors while the movement of the gear after it has passed through the open doors will close them. When the gear is fully extended, doors 'Ill and l5 are thereby closed and locking mechanism 3 l is automatically moved into the locking position with the aid of bungee spring d5.

The most critical period of operation of the gear is of course when landing the aircraft. When the wheels first contact the ground, due to the forward velocity of the aircraft, they are caused to spin-up, that is, to start rotating at a peripheral speed equal to the forward velocity of the aircraft. This induces very large dynamic drag forces in the gear and gear reaction structure which, if uncontrolled, will set up high frequency vibrations resulting in rapid deterioration of the strength giving properties of the metal as hereinbefore described.

Drag strut 8 is adapted to absorb-the dynamic drag loads and eliminate the accompanying vibratory oscillations. This is eii'iciently accomplished by the air-oil shock absorber l2. The air in the reservoir chamber is under sumcient pressure to prevent axial movement of piston rod 22 relative to housing I under static load conditions, but will allow relative movement therebetween upon application of dynamic loads. When the piston moves from the static load condition shown in Figure 2, oil is forced through orifice 28 and into the chamber on the opposite side of the piston. Since a volume reduction occurs, some of the oil in the piston chamber will also flow into the reservoir chamber through the orifice in bulkhead Il. The greater piston area being on the reservoir side, the air pressure tends to return the piston to its static load position. This motion is controlled by the passage of oil back through orifice 28 from the space provided by the initial movement of the piston. The rate at which iiuid is allowed to flow through the orifice controls the damping action of the shock absorber so as to prevent repeated oscillations.

The action of the shock absorber obviously causes the drag strut to increase in length which in turn causes the main oleo to swing rearwardly. This of course causes relative movement between the entire gear and its supporting structure. By using the compensating mechanism as shown in Figure 4, the position of retraction cylinder 53 is controlled by relative movement between the piston member 22 and housing l5 of the shock absorber to x its movement with respect to the gear. Thus as the gear pivots rearwardly, the retraction cylinder 53 moves downwardly in accordance with the movement of arm T3, thereby eliminating the possibility of member 56 rotating crank shaft 36 and unlocking the gear.

Since the door is maintained in its closed position when the gear is down by a force produced in spring S2, movement of main oleo 4, caused by the shock absorber, will not affect the operation of the doors. They will be held in closed position by a substantially constant spring force.

To retract the gear, retracting cylinder 53 is actuated so as to cause member 56 to move axially into the housing of the retracting cylinder. The initial movement of member 56 rotates crank shaft 36 which causes pin 38 to be drawn back out of contact with member 34 and at the same time, causes compression bungee 49 to overpower tension bungee 45 and Vunlock mechanism 3l to allow the gear to begin retracting upon further actuation of retracting cylinder 53. The initial retracting movement of the gear pushes on rods 88 to cause doors 'i4 and 15 to open so that the main oleo may pass through the opening thus provided. As the gear passes through the opening and out of the slipstream, the pivot locations are such that a pull force is applied to rods for closing the doors. When the gear is fully retracted, the doors are again in closed position and members 33 and 34 of locking mechanism 3| swing into co-aXial, locked alignment with the assistance of bungee spring 45.

Though the landing gear is described in considerable detail as a main gear connected to the aircraft wing structure, it obviously is equally useful as a nose gear as well as a main gear and is not limited to any specific location on the aircraft. It is to be further understood that certain changes, alterations, modifications and substitutions can be made to the described structure without departing from the spirit and scope of the appended claims.

We claim as our invention:

l. A retractable landing gear for an aircraft having a door adapted to open only while raising and lowering said gear and wherein the movenient of said gear operates said door comprising, a main oleo pivotally carried by said aircraft, a shock absorbing drag strut pivotally connected to said oleo and to said aircraft, said strut being allowed limited telescopic movement for absorbing shock loads in said gear, a locking mechanism connected at one end to said strut and at its opposite end to said oleo, an actuating cylinder connecting with said locking mechanism for raising and lowering said gear, said locking mechanism being operated by relative movement between said actuating cylinder and said oleo. a compensating mechanism carried by said aircraft and connecting with the free end of said actuating cylinder, said compensating mechanism being responsive to telescopic movement of said drag strut for maintaining said actuating cylinder and said oleo in substantially fixed relative positions irrespective of gear movement due to shock loads, and means connecting with said oleo and said door maintaining said door in closed position in both retracted and extended positions of said gear irrespective of telescopic movement in said drag strut.

2. An aircraft landing gear of the retractable type having a shock absorbing drag strut, actuating means mounted therewith for raising and lowering said gear, locking means carried by said gear and responsive to relative movement between said actuating means and said gear for locking said gear in down position, and compensating means connecting with said strut for maintaining said actuatng means and said locking means in substantially fixed relative positions irrespective of relative movement between said gear and aircraft due to variations in the length of said strut in absorbing shock loads whereby dependable automatic operation of said locking means is obtainable.

3. A retractable landing gear for aircraft comprising an oleo pivotally carried at one end thereof by said aircraft, a drag strut connecting at one end to said aircraft and at its opposite end to said oleo, said strut including a shock absorber having a generally tubular housing forming a piston chamber and a reservoir chamber in coaxial alignment, a piston carried within said piston chamber, a piston rod extending axially into'said housing and rigidly connecting with said piston, orifices providing pressurized fluid communication between said chambers and through said piston, said piston having a greater working area on one side thanon the other tending to maintain it in an extreme axial position within said piston chamber due to fluid pressure, said rod extending axially beyond said housing providing one end of said strut, an armconnecting with the free end of said housing providing the opposite end of said strut, a locking mechanism carried by said gear, an actuating cylinder supported by said aircraft and connecting with said locking mechanism for raising and lowering said gear, said locking mechanism being responsive to relative movement between said actuating cylinder and said oleo for locking and unlocking said gear, and compensating means connecting with said strut and actuating cylinder for maintaining said actuating cylinder fixed relative to said oleo irrespective of axial movement of 'said drag strut to prevent inadvertent unlocking of said gear.

4; A retractable landing gear for an aircraft comprising, a wheel supporting member pivotally carried at one end thereof by said aircraft, a drag strut including a piston rod pivotally connecting at one end with said aircraft, a stepped piston formed on the free end of said rod, piston having a larger working area on one side than on the other, a generally tubular housing having a piston chamber and an annular reservoir chamber, said housing being adapted to receive said piston and rod and allow limited axial movement thereof relative to said housing upon application of dynamic loads, said piston land reservoir chambers being fiuid tight and in communication with one another so as to allow fluid under pressure to ow into and out of the piston chamber, an orifice through said piston for allowing huid flow therethrough on either side thereof upon axial movement of said rod relative to said housing, an arm pivotally connecting at one end with the free end of said housing and at its opposite end to said wheel supporting member, a toggle link connecting at one end with said Wheel supporting member and at its opposite end with said drag strut for limiting the movement of said gear, locking means carried by said toggle link for locking said gear in extended and retracted positions, and actuating i sans connecting with said locking mechanism and said aircraft for raising and lowering said gear and for operating said locking mechanism.

5. A retractable landing gear for an aircraft having a door adapted to open only while raising and lowering said gear and wherein the movement of said gear operates said door comprising, an oleo pivotally carried by said aircraft, a drag strut including a piston rod pivotally connecting with said aircraft, a stepped piston formed on the free end of said rod having a larger working area on one side than on the other, a housing having a piston chamber and an annular reservoir chamber, said housing being adapted to receive said piston and rod and allow limited axial movement thereof relative to s housing, oriiices allowing pressurized huid communication between said chambers and on either side of said piston for absorbing dynamic shock loads, an arm pivotally connecting with the free end of said housing and extending to connect with said oleo, a locking mechanism connecting with said strut and oleo for locking said gear. in extended :and retracted positions, an actuating cylinder connecting with said locking mechanism for raising and lowering said gear, said locking mechanism being adapted for automatic locking and. unlocking by relative movement between said cylinder and oleo, a compensating mechanism carried by said aircraft and operable by relativemovement between said piston rod and housing and adapted to support said actuating cylinder so as to maintain a Ahxed position thereof relative to said oleo irrespective of relative movement between said piston rod and housing so as to prevent inadvertent unlocking of said gear, and means associated with said oleo including a spring for maintaining a substantially constant closing force on said doors when saidgear is extended irrespective of telescopic movement of said strut, and a rigid mechanicallinkage for operatingsaid door and maintaining it in closedr position when said gear is retracted.

6. A self-contained air-oil shock absorbing drag strut for anraircraft landing gear comprising ay generally tubular housing, a transverse bulkhead rigidly fixed within said housing and forming a reservoir chamber and a piston chamber, a piston carried within said piston chamber and adapted for limited axial movement therein relative to said housing, a piston rod extending axially into said housing and connecting with said piston, said piston having a greater working area on one side than on the other whereby liquid under pressure tends to maintain said piston in an extreme axial position within said piston chamber, a chamber orifice providing fluid communication between said chambers and controlling the movement of said piston due to dynamic shock loads, and means including a piston orifice providing fluid communication through said piston and controlling the return stroke movement of said piston to eliminate oscillations induced by said dynamic shock loads.

7. A retractable landing gear for aircraft coinprising a wheel supporting member pivotally connected at one end to said aircraft, a resilient shock absorbing drag strut pivotally connected at one end to said aircraft and at its opposite end to said wheel supporting member, locking means carried by said gear, actuating means connecting with said locking means for raising and lowering said gear, said locking means being responsive to relative movement between said actuating means and said locking means for locking and unlocking said gear, and compensating means carried by said aircraft and responsive to changes in the length of said strut due to loads for supporting said actuating means and maintaining said actuating means and said locking means in substantially ixed relative positions irrespective of said changes in the length of said strut whereby dependable automatic operation of said locking means is obtained.

8. A retractable landing gear for an aircraft having a door adapted to open only while raising and lowering said gear and wherein the movements of said gear operates said door comprising an oleo pivotally carried by said aircraft, a shock absorbing drag strut connected at one end to said aircraft and at its opposite end to said oleo, actuating means associated therewith for raising and lowering said gear, locking means carried by said gear and responsive to relative movement between said actuating means and said gear for locking said gear in down position, compensating means connecting with said strut for maintaining said actuating means and said locking means in substantially xed relative positions irrespective of relative movement between said gear and aircraft due to shock absorbing action of said strut, and means connecting with said gear and said door maintaining a substantially constant closing force on said door in both extended and retracted positions of said gear irrespective of gear movement due to the action of said strut upon application of dynamic drag loads.

9. A retractable landing gear for aircraft comprising, a wheel supporting member pivotally connected at one end to said aircraft, a drag strut connecting at one end to said aircraft and at its opposite end to said wheel supporting member, said strut including a shock absorber, said shock absorber including a generally tubular housing, and a piston rod adapted to be received by said housing and extend axially therefrom to form a part of said strut, said piston rod being adapted for limited axial movement relative to said housing for damping vibrations due to shock loads, a locking mechanism associated with said strut for locking said gear in its extended position, actuating means connecting with said locking mechanism for raising and lowering said gear,

said locking mechanism being responsive to relative movement between said actuating means and said locking mechanism for unlocking said gear, compensating means connecting with said housing and being xed with respect to said piston rod for supporting said actuating means, and maintaining said actuating means iixed relative to said locking mechanism irrespective of relative movement between said piston rod and housing whereby inadvertent unlocking of said gear due to the application of dynamic drag loads is eliminated.

ALBERT E. KANODE.

CONRAD H. COOKE.

FREDERICK V. LINDQUIST,

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,864,134 Harris June 21, 1932 2,467,015 Dreifke Apr. 12, 1949 2,559,451 McBearty July 3, 1951 

